Re: [Vala] Treating a uint as a reference type?

[Mario Daniel Ruiz Saavedra <desiderantes rocketmail com>]

Maybe defining an IntegerRank it would work

Enviado desde Yahoo Mail en Android

De:"Alan Manuel Gloria" <almkglor gmail com>
Fecha:jue., jul. 30, AM a 10:28 AM
Asunto:Re: [Vala] Treating a uint as a reference type?

I tried that, but it loses the automatic insertion of ref and unref
function calls.  The entity_dup and entity_free functions are never called
in the example I gave, and Vala complains that it can't transfer ownership
using (owned) - there is no reference to transfer.

Semantically, an Entity is a reference to a row in an entity component
system; it just happens to be implemented using uint.  I want to do this
because when I delete a row in the ECS table, I want the row to be retained
as "deleted" until all references to it are dropped, so that I avoid the
"missile suddenly chases a new entity" problem.



On Thu, Jul 30, 2015 at 10:56 PM, yannick inizan <inizan yannick gmail com>
wrote:

> why don't you "subclass" uint ?
>
> public struct Entity : uint {
> // these methods are required at C-side.
> internal Entity dup() { return this; }
> internal void free() { delete &this; }
>   // your code
> }
>
> 2015-07-30 16:43 GMT+02:00 Alan Manuel Gloria <almkglor gmail com>:
>
> > Hi Vala World,
> >
> > I was wondering if it's possible to implement a Vala class as a C-side
> > guint, but have Vala emit calls to a ref and unref function, and to treat
> > a
> > C-side 0 as a Vala-side null.
> >
> > Basically I want to make something like this:
> >
> > // Vala
> > static
> > Entity? mine = null;
> >
> > static
> > void
> > set_mine(owned Entity e) {
> >   mine = (owned) e;
> > }
> >
> > static
> > void
> > do_stuff() {
> >   Entity e = Entity.create();
> >   set_mine(e);
> > }
> >
> > And get it compiled to C:
> >
> > /* C */
> > guint mine = NULL;
> > void
> > set_mine(guint e) {
> >   if (mine != NULL) entity_unref(mine);
> >   mine = e;
> > }
> >
> > void
> > do_stuff() {
> >   guint e = entity_create();
> >   set_mine(entity_ref(e));
> > }
> >
> > So far, I've tried using a [Compact][CCode (cname="guint")] class, but
> > that
> > is passed around as a guint* and Vala feels obliged to add a "typedef
> > struct _guint guint". which fails since guint is already defined as
> > unsigned int.
> >
> > I've also tried using a [CCode (cname="guint")] extern struct, but that
> > causes any ref_function and unref_function attributes to be ignored, and
> > still adds "typedef struct _guint guint".
> >
> > Is it possible to have Vala remove the "*" in reference types and still
> > have it use ref/unref functions and have it remove typedef?
> >
> > --
> >
> > I'm trying to make an Entity Component System, and ensure that destroyed
> > entities are not reused until all references to them are destroyed.
> > Entities are normally implemented as simple integer ID's, which are
> > semantically a pointer to a row of component slots.
> >
> > My current design has each attached component add a reference to the
> > entity, and the entity manager also adds a reference; when an entity is
> > destroyed, the entity manager detaches all components (which cause each
> > component to drop the reference) and drops its own reference; this frees
> > the entity unless another reference is kept elsewhere.  If a reference to
> > an entity is kept elsewhere, it can then be queried as to whether it has
> > been destroyed without worrying that its ID has been re-allocated to a
> > freshly-made entity (for instance, consider a missile locked on to some
> > game entity; if the target dies, we want the missile to know it has no
> > longer any valid target, not have it suddenly chase another entity that
> > happened to get allocated the same ID as the missile's original target in
> > a
> > different subsystem).
> >
> > In my current design entities are compact classes with an ID and a
> > refcount
> > and custom ref_function and unref_function, and freed entities are
> > retained
> > in a freelist to reuse the ID.  I was wondering if I could make entities
> > just the ID itself, and store the refcount in a separate array.
> >
> > I could possibly live with passing around Entity*, and use (guintptr) to
> > extract the ID from the pointer, but I worry since C does not guarantee
> > that a pointer can retain all possible guintptr values.  guintptr can hold
> > any pointer type, but a pointer type is not necessarily capable of holding
> > any guintptr.
> >
> > Sincerely,
> > AmkG
> > _______________________________________________
> > vala-list mailing list
> > vala-list gnome org
> > https://mail.gnome.org/mailman/listinfo/vala-list
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